1. Field of the Invention
This invention relates to multicomponent alloys for use in hydrogen storage, hydride heat pump and rechargeable hydrogen storage electrode applications. More particularly, the invention relates to rechargeable batteries comprising a nickel-hydride, or silver-hydride couple in which the negative electrode is the hydride/hydrogen storage electrode.
2. Description of the Related Art
The present invention is an improved hydrogen storage and/or hydride electrode alloy derived from the materials described in U.S. Pat. Nos.: 4,370,163; 4,551,400; 4,716,088; 4,728,586; 4,946,646; 4,849,205; 5,006,328; 5,096,667; and 5,104,617. These patents reported multicomponent alloys containing oxygen sensitive metals such as titanium, vanadium and zirconium. These metals are very active and always form oxide layers on their surface. During the alloy preparation at high temperature, they are particularly sensitive to oxygen in the melting chamber and oxidize with the other substances in the melting furnace. As a result, the quality of the alloys obtained are somewhat not as good as expected. Furthermore, the alloy powder and the electrode made therefrom are sensitive to the oxygen in the environment at every process stage such as sintering, pasting and charging/discharging in alkaline solution. Moreover, some alloys might have high capacity, but they are not easy to activate and/or maintain operational life. Consequently, the electrochemical properties such as rate capability, charging efficiency and cycle life will suffer badly. And, for gas hydrogen storage or purification applications, they are more easily poisoned by impurity gases. Thus, capacity and life drop. For hydride heat pump applications, oxide formation will increase the hysteresis leading to difficulty for the hydride pair to match and the efficiency reduces substantially.
Very recently, U.S. Pat. No. 5,242,656 on Sep. 7, 1993 was issued to Zhang et al. Zhang disclosed two group of hydride electrode materials: 1)a CaNi.sub.5 -type alloy, M.sub.m Ni.sub.5-x-y-z-u A.sub.x B.sub.y C.sub.z D.sub.u, where M.sub.m is mischmetal, A equals Mn, Sn, or V; B equals Cr, Co, Ti, Zr, or Si; C equals Al, Mg, or Ca; D equals Li, Na, or K; and 0.ltoreq.x.ltoreq.0.95, 0.ltoreq.y.ltoreq.1, 0.ltoreq.z0.7, 0.1.ltoreq.u.ltoreq.0.9; and 2) a ternary alloy, Ti.sub.2 NiD.sub.u, where D equals Li, Na, or K; and 0.04.ltoreq.u.ltoreq.0.9. Zhang described their materials as having a better result because of the inclusion of Li, Na or K. However, while these two groups are different from the multicomponent alloy systems mentioned above, they do not solve the aforementioned problems.
To solve these problems, the present invention provides new alloys for hydrogen storage and in particular for rechargeable hydride electrodes for battery applications.